Kim Myung Soo aka L (23 years old)

He used to be a warm, clever, good and most of all, handsome student. He was loved by everyone, except the boys who envy him. But things changed, when the girl he loves left him without any word but her confession, since then a 180 degree change occurred on him. He becomes a bad boy, flirting with girls, jelling hair, going to club, convert to a total playboy. He reveals to no one the reason he changed, except his best friends, INFINITE.

Jung Soo Jung aka Krystal (20 years old)

She is a sweet, clever girl, passionate to music, and worshiped Christina Aguilera. For her dreams, she even left the familiar Korea and went to U.S.A. study. After graduation, she came back to Korea, but in another identity. When she left, she thought memories here should be cut, including her first love and precious friendship. On the day she quit school, she left a confession letter to her lover. No one knows what happened to her after she left school, including her best friends f(x), until her come back, and contact them. 

INFINITE:

Kim Sung Gyu (26 years old)

Jang Dong Woo (24 years old)

Nam Woo Hyun (24 years old)

Hoya Lee Ho Won (24 years old)

Lee Seong Yeol (23 years old)

Lee Sung Jong (21 years old)

f(x):

Victoria, Song Qian (28 years old)

Amber Liu (22 years old)

Luna Park Sun Young (21 years old)

Sulli Choi Jin Ri (21 years old)

Other female students:

SNSD 

BoA

Other male students:

EXO

Super Junior

Shinee